"Pet" Compounds - PS and HDPE

Polystyrene (PS):

     Second only to polyethylene, polystyrene is one of the most common inexpensive, rigid plastics in everyday life.  It is a polymer with "thermoplastic properties, and it is created from the petroleum-derived monomer, styrene". It is important to note that several different types of this compound are produced:

Extruded polystyrene:  This form of polystyrene is purported to have as much "tensile strength as unalloyed aluminum, but it is lighter and more elastic".  This variation of polystyrene is used in manufacturing an array of molded products such as plastic tableware, yogurt cups, CD cases, and model cars.  

Extruded polystyrene foam: Also known as Styrofoam, this form of polystyrene has numerous applications in many facets of urban life and manufacturing.  It may also be used in building materials or in roadway construction.  For example, "it may serve as a layer of insulation under pavement to prevent freezing and thawing of the soil below from cracking the surface".  

Expanded polystyrene foam:  In this form, polystyrene is essentially comprised of expanded polystyrene beads.  It is this type of material that is used to create "peanuts" for packaging, disposable coolers, and takeout boxes.






Here is a clip from How It's Made pertaining to the manufacturing of expanded polystyrene products:

  
Source: http://www.wisegeek.com/what-is-polystyrene.htm


High-Density Polyethylene (HDPE):

     This compound, similar to polystyrene, is a type of plastic that derives from petroleum.  It is a material that can be re-molded by melting and shaping, and, in addition, it can be joined in segments when welded or machined. As understood from its name, high-density polyethylene is much denser than most other polymer plastics.  The reason for this is due to "its crystallization structure occurring in a linear fashion rather than branching out to form long chains of polyethylene".  The result of this lack of branching is increased bondage between its carbon molecules and hydrogen molecules.  This provides the final product to possess greater tensile strength, even though it is lighter than water.  This structure also makes high-density polyethylene highly resistant to acids and solvents.  


Applications of HDPE:


Due to the fact that high-density ethylene is so durable and chemically non-reactive, it is used in many aspects of industry and manufacturing.  Here are a few uses of HDPE:

1. Utilized in many different packaging containers, such as milk and laundry detergent bottles
2. Plastic grocery bags
3. Found in storage systems designed to store chemicals and fuels.
4. Used to produce materials that act as chemical barriers, such as liners that are placed under landfills to help prevent soil and groundwater contamination.

The most common utilization of HDPE, though, is in the "manufacturing of wood plastic composites to make furniture, flooring, fencing, and landscaping materials".  

Here is a quick video about HDPE:

Source: http://www.wisegeek.com/what-is-high-density-polyethylene.htm